Lately, fuel propelled engines have been proposed for scooters, motorcycles and go-carts for use in daily life. These are typically light weight, easy to use and inexpensive vehicles, generally for use under favorable weather conditions. Simple fuel propelled engines proposed for driving these vehicles however, do not have complicated systems other than a basic throttle mechanism for changing the rpm (revolution per minute) of the motor. Mostly, a basic throttle mechanism has a limited capability to adjust the speed of the vehicle in the absence of a transmission that can shift the rpm transmitted to the drive wheel(s). Electric motors, as an alternative power source, do likewise have drive circuits that add on to the price of the vehicle and can serve only in limited ranges for changing the speed of the vehicle. Furthermore, they are restricted with the characteristics of the motor and of course, the batteries carried on the vehicle. The purpose behind these limitations is to restrict the weight of the vehicle as well as to reduce the price associated with complex speed varying systems in both types of motors. Nevertheless, users still feel the need to change the speed of the vehicle or torque applied on the driving wheel at varying times. If the vehicle route is generally smooth and presents low resistance to vehicle passage, riders generally complain on the relatively low vehicle speed and desire to ride at higher speeds. In other cases e.g. where the vehicle route presents high resistance to vehicle passage or comprises hills, users generally complain that the vehicle is incompetent to comfortably climb the hill at varying inclination. At this point, a mechanical shifting system which only slightly contributes to weight of the vehicle and which effectively serves both needs (high speed on smooth surfaces and high torque on hill climbing) without add on installation on the motor or an extra amount on the price of the vehicle is needed.
A further restriction on the transmission systems for scooters, go-carts or motorcycles is the fact that there is generally very limited space on the vehicle. An ideal system is the one that occupies minimum volume in between the drive wheel and the propulsion system. Moreover, it should be noted that in cases where the transmission system comprises a plurality of moving or rotating parts, their inertia adversely affect the dynamic stability of the vehicle especially during shifting, which is an undesired effect of such transmission systems.
Various transmission systems have been proposed so far for scooters, go-carts or motorcycles that are driven directly or indirectly by a motor, generally an electric motor or fuel propelled engine. Among these, chain transmissions, gear transmissions or fluid operated transmissions are conventional ones and already known for long decades. In addition thereto, direct drive transmission systems were developed to reduce mechanical losses arising from the presence of a transmission mechanism comprising a plurality of moving parts. Direct drive transmission systems comprise an actuator which is directly in contact with the driving wheel(s) of a vehicle and do lack a belt or gear driven transmission element that could result in loss of kinematic energy, generally by way of friction losses. As the transmission system of the present invention relates to direct drive systems, the following documents have been considered as relevant.
BE 1002860 A (Meulebroecke, 1989) discloses a bicycle equipped with an auxiliary transmission system driven by a battery operated electric motor. The auxiliary transmission system proposed by Meulebroecke comprises a conical actuating member that is directly in contact with the driving wheel and that enables the user to continuously vary the speed of the bicycle. The battery operated electric motor and the conical actuating member is guided on a rod which is fixedly attached to the chassis of the bicycle and which allows for axial movement of entire drive unit, i.e. the battery operated electric motor and the conical actuating member. Once the drive unit moves axially on its guide, the conical actuation member contacts the tire at a varying location on its outer perimeter and changes the rpm transmitted onto the drive wheel. A major problem associated with this type of drive systems is the need to move back and forth entire driving mechanism including the motor and the transmission element i.e. the conical actuation member and possibly, the batteries. High mass of these parts pose a threat that is likely to impede effective working of the drive unit and to differentiate the speed applied on the drive wheel. In addition, inertia of the entire drive system and the need to change its location during driving inadvertently affect the kinematic stability of the vehicle to which this proposed drive system is installed. A further drawback of this transmission system proves itself in the difficulty of moving a relatively heavy motor, transmission element and couplings of the same with the aid of a simple protrusion cable through which a wire is proposed to readily slide for moving back and forth the entire drive unit.
U.S. Pat. No. 3,891,044 (Tiede, 1973) discloses a drive system similar to that of Meulebroecke where the drive wheel is driven by one or two cone shaped rollers which contact the tire from its lateral surfaces. Likewise, the entire drive unit is proposed to move transitionally to change the rpm of the drive wheel during ride. Another drawback is based on the fact that the rider has to remove one of his hands from the handlebar of the vehicle and command the transmission system, which is a possible threat against the safety of the ride. Complex structure and multi axial movement requirements of the transmission system proposed by Tiede are likely to produce frequent breakdowns and high maintenance costs. Most of the drawbacks of the transmission system as proposed by Meulebroecke in the preceding paragraph also do apply to the transmission system of Tiede.
DE 9205672 U (Hofberger, 1992) shows a drive system that comprises a stepped actuation member coupled to a battery operated motor and a mechanism to engage and disengage the drive system onto the tire of the bicycle. The mechanism requires the user to pull a rod that moves the entire group of transmission elements, the electric motor and the stepped actuation member, which after sufficient displacement, is pressed against the traction surface of a drive wheel. High inertia of the entire drive system is one of the major drawbacks of this drive unit as the total inertia of the entire drive and transmission organs is likely to impede easy shifting operation and to disrupt stable movement of the vehicle. Most of the drawbacks of the transmission system as proposed by Tiede in the preceding paragraph also apply to the transmission system of Hofberger.
U.S. Pat. No. 4,081,048 discloses a friction drive for a vehicle wherein a friction drive wheel is mounted to engage frictionally the pneumatic tire constituting the periphery of a vehicle traction wheel, such drive wheel being carried on a strut mounted to swing about an axis remote therefrom and which is parallel to and spaced from the axis of the traction wheel in an arrangement such that the strut is subjected to a reaction torque in response to driving friction force in one direction which in turn urges the center of the drive wheel towards the center of the ground wheel. The drive wheel is of frusto-conical configuration so that a variation in drive ratio can be driven by a storage battery.
US 2004/0055803 A1 (Patmont, 2003) discloses a variable speed transmission for a scooter. The transmission of Patmont foresees use of two inter-engaging parts that press onto the drive tire and that change the rpm applied on the tire by way of changing the outer diameter of the engaged parts. Keeping in mind that these inter-engaging parts are movable parts that are primarily responsible for transmitting the rotational power or the torque applied onto the drive wheel, those skilled in the art will readily appreciate how difficult it is to implement such an embodiment, if not inapplicable at all. High maintenance requirement of the system as well as the excessive wear expected on the traction surface of the tire are among other drawbacks of the transmission system proposed by Patmont. In addition, Patmont fails to teach a mechanism that enables shifting during ride.